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Discussion Groups | LPC2000 | Problem with ADC
Discussion group dedicated to the Philips LPC2000 family of ARM MCUs
Problem with ADC - shakeel_qau - Jul 24 0:52:46 2008
Hi
i am using lpc2368,with ADS v1.2 ,i am facing problem with A to D
conversions.i get the right values in ADC for given analog input if i
use VREF 3.3v ,as soon as i change reference to 1.2v the values i read
from ADC are not correct for given analog input even at 0v input,plz
help
Shakeel
------------------------------------
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i am using lpc2368,with ADS v1.2 ,i am facing problem with A to D
conversions.i get the right values in ADC for given analog input if i
use VREF 3.3v ,as soon as i change reference to 1.2v the values i read
from ADC are not correct for given analog input even at 0v input,plz
help
Shakeel
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
Re: Problem with ADC - Albert Bartoszko - Jul 25 13:44:16 2008
Dnia 2008-07-24, czw o godzinie 04:52 +0000, shakeel_qau pisze:
> Hi
> i am using lpc2368,with ADS v1.2 ,i am facing problem with A to D
> conversions.i get the right values in ADC for given analog input if i
> use VREF 3.3v ,as soon as i change reference to 1.2v the values i
> read
> from ADC are not correct for given analog input even at 0v input,plz
> help
>From LPC2368 Product data sheet:
ADC reference: This should be nominally the same voltage as VDD(3V3) but
should be isolated to minimize noise and error.
Albert
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
> Hi
> i am using lpc2368,with ADS v1.2 ,i am facing problem with A to D
> conversions.i get the right values in ADC for given analog input if i
> use VREF 3.3v ,as soon as i change reference to 1.2v the values i
> read
> from ADC are not correct for given analog input even at 0v input,plz
> help
>From LPC2368 Product data sheet:
ADC reference: This should be nominally the same voltage as VDD(3V3) but
should be isolated to minimize noise and error.
Albert
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
Re: Problem with ADC - wvanhoomissen - Jul 25 22:38:25 2008
>From NXP website
"Generic questions
Q: On the LPC2xxx, the analog power pin (V3A) states that it should
be nominally the same as the V3 pin, but can I connect a precision
reference to this V3A pin that is at less voltage than the V3 pin or
am I forced to use the same 3.3V power supply that I use on V3?
A: The ADC voltage can go below 3V. According to test, the ADC
operates according to spec even below 2V. "
It looks to me like it quits working somewhere bewteen 2 and 1.2V.
I see an opamp in your future.
--- In l...@yahoogroups.com, "shakeel_qau"
wrote:
>
> Hi
> i am using lpc2368,with ADS v1.2 ,i am facing problem with A to D
> conversions.i get the right values in ADC for given analog input
if i
> use VREF 3.3v ,as soon as i change reference to 1.2v the values i
read
> from ADC are not correct for given analog input even at 0v
input,plz
> help
> Shakeel
>
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
"Generic questions
Q: On the LPC2xxx, the analog power pin (V3A) states that it should
be nominally the same as the V3 pin, but can I connect a precision
reference to this V3A pin that is at less voltage than the V3 pin or
am I forced to use the same 3.3V power supply that I use on V3?
A: The ADC voltage can go below 3V. According to test, the ADC
operates according to spec even below 2V. "
It looks to me like it quits working somewhere bewteen 2 and 1.2V.
I see an opamp in your future.
--- In l...@yahoogroups.com, "shakeel_qau"
wrote:
>
> Hi
> i am using lpc2368,with ADS v1.2 ,i am facing problem with A to D
> conversions.i get the right values in ADC for given analog input
if i
> use VREF 3.3v ,as soon as i change reference to 1.2v the values i
read
> from ADC are not correct for given analog input even at 0v
input,plz
> help
> Shakeel
>
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
Re: Problem with ADC - ksdoubleshooter - Jul 28 11:36:14 2008
Per the data sheet, the minimum voltage for VREF is 2.5v.
Jeff
--- In l...@yahoogroups.com, "shakeel_qau" wrote:
>
> Hi
> i am using lpc2368,with ADS v1.2 ,i am facing problem with A to D
> conversions.i get the right values in ADC for given analog input if
i
> use VREF 3.3v ,as soon as i change reference to 1.2v the values i
read
> from ADC are not correct for given analog input even at 0v input,plz
> help
> Shakeel
>
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
Jeff
--- In l...@yahoogroups.com, "shakeel_qau"
>
> Hi
> i am using lpc2368,with ADS v1.2 ,i am facing problem with A to D
> conversions.i get the right values in ADC for given analog input if
i
> use VREF 3.3v ,as soon as i change reference to 1.2v the values i
read
> from ADC are not correct for given analog input even at 0v input,plz
> help
> Shakeel
>
------------------------------------
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )